What is called a polyolefin wax containing a low molecular weight olefin polymer is used in a wide range of applications including a coating agent in an emulsion form, a solution form or the like, a mold releasing agent used together with a toner or the like, a resin modifier, a hot melt adhesive and the like.
Since a polyolefin structure basically has no polar group, it is used, in many cases, in combination with a nonpolar or low-polar component. It is known that polar groups are difficult to directly introduce into a polyolefin because a transition metal catalyst working as a catalyst in olefin polymerization is poisoned by such polar groups to largely degrade the polymerization activity.
As a method for producing a polyolefin wax, not only a method in which an olefin is lowly polymerized by using the above-described transition metal catalyst but also a method in which a highly polymerized olefin polymer is thermally decomposed is known.
When a polyolefin wax is used in combination with a resin having polarity such as an acrylic or an engineering plastic, it is preferable, in many cases, to introduce polar groups into the polyolefin wax. As a method for introducing polar groups, a method in which the polyolefin wax is oxidized in air, and a method in which the polyolefin wax is reacted by using a radical initiator in the presence of a polar compound having a double bond such as maleic anhydride are known (see, for example, PTL 1).
PTL 2 discloses that, as a method for introducing a polar group into a wax having 3 or more carbon atoms such as a propylene wax, a method in which a polyolefin wax obtained by direct polymerization using a transition metal catalyst or the like is reacted with a polar compound having a double bond such as maleic anhydride is preferred. Further, PTL 2 discloses that when a polypropylene wax obtained by thermal decomposition is subjected to a radical reaction with maleic anhydride, viscosity unavoidably increases. Furthermore, PTL 2 and the like disclose that when a propylene-based wax is oxidized in air, it is predominantly decomposed, and hence the resultant easily becomes oily.
On the other hand, recently, there is a tendency of demanding a polyolefin wax having a low melting point in the market. This tendency is accompanied by a tendency of considering significance of energy saving. Specifically, when the melting point of a wax is lowered, it is presumed that the following effects can be expected. When the wax is used, for example, in a toner, the temperature of a fixing drum of a copying machine can be lowered; or when the wax is used in a hot melt adhesive, the adhesion temperature of the hot melt adhesive can be lowered.